106 research outputs found

    Targeted and Reversible Blood-Retinal Barrier Disruption via Focused Ultrasound and Microbubbles

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    The blood-retinal barrier (BRB) prevents most systemically-administered drugs from reaching the retina. This study investigated whether burst ultrasound applied with a circulating microbubble agent can disrupt the BRB, providing a noninvasive method for the targeted delivery of systemically administered drugs to the retina. To demonstrate the efficacy and reversibility of such a procedure, five overlapping targets around the optic nerve head were sonicated through the cornea and lens in 20 healthy male Sprague-Dawley rats using a 690 kHz focused ultrasound transducer. For BRB disruption, 10 ms bursts were applied at 1 Hz for 60 s with different peak rarefactional pressure amplitudes (0.81, 0.88 and 1.1 MPa). Each sonication was combined with an IV injection of a microbubble ultrasound contrast agent (Definity). To evaluate BRB disruption, an MRI contrast agent (Magnevist) was injected IV immediately after the last sonication, and serial T1-weighted MR images were acquired up to 30 minutes. MRI contrast enhancement into the vitreous humor near targeted area was observed for all tested pressure amplitudes, with more signal enhancement evident at the highest pressure amplitude. At 0.81 MPa, BRB disruption was not detected 3 h post sonication, after an additional MRI contrast injection. A day after sonication, the eyes were processed for histology of the retina. At the two lower exposure levels (0.81 and 0.88 MPa), most of the sonicated regions were indistinguishable from the control eyes, although a few tiny clusters of extravasated erythrocytes (petechaie) were observed. More severe retinal damage was observed at 1.1 MPa. These results demonstrate that focused ultrasound and microbubbles can offer a noninvasive and targeted means to transiently disrupt the BRB for ocular drug delivery

    Mid-range wireless power transfer with segmented coil transmitters for implantable heart pumps

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    In wireless power transfer systems, the transmitting coil dimensions can substantially affect the transmission range and alignment sensitivity. We found that a transmitting coil with larger inner and outer diameter has a wider transmission range and lower alignment sensitivity. Thus, we developed a larger coil (24¯30 cm2) designed to be embedded in the back of a vest to power DC pumps for artificial hearts or LVADs. To significantly reduce the required voltage, the coil was divided into 8 segments with resonant capacitors. The coil was operated at 6.78 MHz and evaluated with a 5.3-cm diameter receiving coil. A circuit model for the energy coupling coils was developed to predict the output power and efficiency. Having a coil separation of 7.7 cm, the output power and efficiency of the energy coupling coils are higher than 48 W and 80%, respectively. The system was experimentally tested with a DC pump, demonstrating that the proposed coil segmentation technique can significantly reduce the transmitter voltage to a safe level (~10 Vrms)
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